The present invention relates to a liquid-crystal display device having a gap between two substrates and then sealing a liquid crystal into the gap, after which the gap is sealed.
In recent years, the light weight, thinness, and low power consumption of LCDs has resulted in their use in a variety of information products and terminals and in video equipment, and a large part of the LCDs used in such applications are LCD types such as TN (twisted nematic) and STN (super twisted nematic) LCDs.
While the above-noted types of LCDs have been developed for practical use, because they have the problem of a relatively narrow viewing angle, an in-plane switching (IPS) type of LCD having a parallel electrical field has been proposed as an alternate.
IPS LCDs are formed by a substrate onto which opposing comb-shaped electrodes are formed, a substrate onto which electrodes are not formed, and a liquid crystal that is sealed between these two substrates.
More specifically, as shown in the example of FIG. 10, a gap is formed between a transparent TFT substrate 6 of glass, for example, and a color filter (CF) substrate 13, the periphery thereof being sealed with a sealant, and a liquid crystal 10 being sealed within the gap d between the TFT substrate 6 and the CF substrate 13.
A pair of comb-shaped common electrodes 2 and pixel electrodes 3 are formed on an inner surface of the TFT substrate 6, with no electrodes formed on the other (CF) substrate 13.
An orientation film 9 is formed on the inner surface of each of the TFT substrate 6 and CF substrate 13, these orientation films, as shown in FIG. 5, have had oriented (by rubbing) at an angle xcex81, xcex82, respectively for the direction "THgr"3, which is perpendicular to the teeth of the common electrodes 2 and the pixel electrodes 3.
Polarizers 19 are disposed on the outer surfaces of the TFT substrate 6 and the CF substrate 13, the polarization direction of one of the polarizers being the same as the orientation angle xcex81, while the polarization direction of the other polarizer is at an angle xcex82, which is perpendicular to the orientation direction xcex81.
As shown in FIG. 6(a), with no voltage applied between the common electrodes 2 and the pixel electrodes 3, incident light is changed to linearly polarized light by the polarizer 19 on the incident side and, because the polarization direction coincides with the long-axis direction of the liquid-crystal molecules 22, the light passes through the liquid crystal without a change in the polarization direction, so that the polarization direction of light reaching the light-exiting side polarizer 19 is perpendicular to the polarization direction of that polarizer, and therefore the light is blocked.
As shown in FIG. 6(b), when a voltage is applied between the common electrodes 2 and the pixel electrodes 3, an electrical field created between the common electrodes 2 and the pixel electrodes 3 bends the long-axis direction of the liquid-crystal molecules to a direction that is perpendicular to the longitudinal direction of the electrode teeth.
Because of the above action, light which is changed to linearly polarized light by the polarizer 19 is changed during its travel through the liquid crystal 10 to elliptically polarized light by the effect of the refractive index of the liquid crystal 10, and then passes through the polarizer 19.
One method of displaying an image on an LCD such as described above is that, by providing the common electrodes 2 and the pixel electrodes 3 for each pixel, using one of the electrodes as a scanning electrode and the other electrode as a signal electrode, thereby creating a display in the same manner as was done in a simple matrix (XY matrix) LCD in the past.
Another method is similar to that of a TFT (thin-film transistor) active matrix LCD (hereinafter called an AM-LCD) of the past, in which common electrodes 2 and pixel electrodes 3 and a TFT as a switching element are formed on the inner surface of the TFT substrate 6 for each pixel, so as to selectively display each pixel.
In the case of an AM-LCD, there are cases in which, instead of a three-terminal switching clement such as a TFT, a two-terminal switching element such as a diode or varistor or the like is provided.
Because the viewing angle of an IPS type LCD is wide, the demand for these devices is increasing for use in replacing CRT displays used in the past.
In a TN-mode or IPS-mode color liquid-crystal display element such as used in the past, in order to hold the thickness (cell gap) of the liquid-crystal layer, a spacer 23 made of plastic beads or glass fiber was inserted between an electrode substrate 13 having TFTs or a plurality of scanning electrodes and a color filter side substrate 6, thereby establishing a gap for sealing of a liquid crystal 10 between the substrates 6 and 13.
Because the spacers 23, made of plastic beads or the like, is applied over the top of the substrate, the positions of the beads, for example, between the electrode substrate 13 and the color filter side substrate 6 was indeterminate, because of scattering of light by a spacer 23 positioned above a pixel, there was the problem of a reduction in the display quality of the liquid-crystal display element.
Additionally, because the spacers that are applied to the liquid-crystal display element has spherical or bar-shaped pieces, when forming the cell, because of point or line contact with the cell, there is the problem of imparting damage to the orientation film or the transparent electrodes, thereby leading a tendency for display defects to appear.
Because of the damage to the orientation film or transparent electrodes, the liquid crystal becomes contaminated, and, because a process step that applies the spacers uniformly is required, or it is necessary to accurately control the spacer particle distribution, there is the problem that it is difficult with a simple method to achieve a liquid-crystal display element having stable display quality.
Given the above situation, there was proposed, in Japanese Patent No. 2751392 and Japanese Unexamined Patent Publication (KOKAI) No. 10-104606 and 8-262484, a liquid-crystal display device that uses as a spacer a structure formed by the overlaying of colored layers that form color filters.
Because the spacer formed in the above-noted structure does not require the additional processes to fabricating color filters, it enables the fabrication of a color filter at the same cost as in the past, and is expected to gain usage in the future.
In addition to the above technology, a method of forming a spacer was disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 10-82909, whereby a separate spacer was formed on a color filter having the same structure as in the past. In this case, the method used for forming the spacer was that, for example, of patterning an overcoating layer.
In the above-noted method, because it is necessary to add a process step, the cost is higher than in the past. If a color filter having such a spacer is used in a liquid-crystal display device, in a TN-mode liquid-crystal display device, to prevent the transparent electrode in the part of the spacer butted up against the opposing substrate from creating a short circuit with the opposing substrate electrode, it is necessary to form an insulation film on either the opposing substrate or the spacer top part, and further a need to limit the formation position and size of the spacer, thereby making the fabrication of the color filter difficult.
In and IPS-mode liquid-crystal display device, because the opposing substrate has no electrodes formed thereon, there is no limit to the formation position and size of the spacer, so that compared to a TN-mode liquid-crystal display device, the degree of design freedom is large.
FIG. 11 is a plan view showing a color filter having a spacer in an IPS-mode liquid-crystal display device according to the prior art.
In FIG. 11, the reference numeral 24 denotes a spacer that forms a gap between a pair of substrates, and the reference numerals 25, 26, and 27 are red color filter, green color filter, blue color filter, respectively.
As shown in FIG. 11, in an IPS-mode LCD of the past, the color layers 25, 26, and 27 are arranged with colored layers of the same color in a vertically oriented line,.and the color layers 25, 26, and 27 are arranged in a prescribed sequence in the horizontal direction. A spacer 24 is disposed for each green color layer 26, the spacers 24 supporting the substrate and forming a gap between the pair of substrates, between which liquid crystal will be sealed.
In an IPS-mode LCD described above according to the prior art, the spacers 24 are arranged every two pitches in the horizontal direction and every 1 pitch in the vertical direction, forming a tightly packed arrangement, in which the positions at which the substrate is supported by adjacent spacers 24 are in close proximity to one another.
Although the TFT substrate and CF substrate 13 flex in accordance with the changes in the dimensions of the gap caused by thermal expansion and contraction due to changes in the temperature of the liquid crystal 10, because there are a plurality of columnar-shaped spacers 24 as noted above supporting the substrate, the flexures of the TFT substrate 6 and the CF substrate 13 are restricted, leading to the occurrence of a defect in which a gap is formed between the substrates 6 and 13 and the liquid crystal 10 surface. This phenomenon is known as liquid crystal bubbles and, in a liquid-crystal display device having normally closed characteristics, it manifests itself as black display defects, thereby lowering the display quality.
Accordingly, it is an object of the present invention to provide a liquid-crystal display device that solves the above-mentioned problem of liquid crystal bubbles.
In order to achieve the above-noted object, a liquid-crystal display device according to the present invention is one in which a liquid crystal is sealed within a gap established by first spacers between a pair of opposing substrates, wherein a spacing between positions at which the first spacers support said substrates is widened, so that the substrates flex so as to track a dimensional change in the gap caused by a temperature change in the liquid crystal.
In the second aspect of the present invention, of pixels of three colors, the spacers are disposed at positions corresponding to pixels of one color, thereby widening the spacing between positions at which the first spacers support the substrates.
In the third aspect of the present invention, a second spacers having a height that is shorter than the first spacers are provided between the first spacers, the substrate having flexed to track a dimensional change in the gap accompanying a temperature change in the liquid crystal is supported by the second spacers at a height shorter than that of the first spacers, thereby establishing a uniform gap between the substrates.